The present invention relates to relays, and more particularly to relays capable of maintaining a characteristic impedance at microwave frequencies.
A type of relay currently used in microwave applications uses a wiper having a contact trace pattern to provide an electrical connection with a contact trace pattern on a substrate. Such a microwave relay is disclosed in a copending patent application No. 06/728,130 to Grellman, et al, entitled "Integrated Pad Switch". Specifically, FIG. 3 of Grellman discloses a substrate having a microstrip line pattern and a wiper having a contact trace pattern. Rotating the wiper causes the contact trace pattern to establish a different electrical connection with the contact trace pattern on the substrate. This type of switch has excellent high frequency characterisitcs and may be used in attenuator circuits or the like.
The problem with such prior art relay structures lies in the wiper which slides across the substrate as the various electrical connections are formed. In order to have a long operational life and low operating forces, the surfaces of the wiper and the substrate must be very smooth, hard and have low friction. Most common substrates found in hybrid circuits are ceramic and hard, but not smooth, and therefore have relatively high coefficients of friction. A fundamental tradeoff exists between low resistance electrical connections and long operational life. That is, a low resistance electrical connection requires large normal forces to minimize contact resistance which leads to excessive wear and short operational life, whereas long operational life mandates small normal forces which produces a poor electrical connection.
Therefore, what is desired is a microwave relay which has excellent frequency characteristics, yet achieves this performance without excessive wear between the wiper and the substrate, leading to long operational life.